Transmitter



vMarch 4, .1941. F, KAESER 2,233,453

TRANSMITTER Filed April 8, 1958 Patented Mar. 4, 1941 Siemensa Halske, Aktiengesellschaft, Siemensstadt,V Berlin, Germany, a corporation of Germany Application April 8, 1938', Serial No. 200.856' In Germany April17,.193 7:

5 anims.

In modulator arrangementsv there occur with constant grid biasing potential Variations of the high-frequency voltage furnished and variations of the degree of modulation. It is known that when feeding thel modulation arrangement from an A. C. network to also derive the biasing grid potential of the modulation tube from the network by means of' a rectifier. Furthermore, it is also known to apply a fixed grid biasing potential in series to the biasing potential which varies with the voltage of the network. With this arrangement, variations ofthe plate potential can be compensated such that theV delivered' highfrequency voltage and the degree of' modulation 1 remain constant.

The variations of the operating4 voltage in tube transmitters having separate oscillator and modulator may be compensated for by using for the biasing potential of the modulation tube a voltage varying with the network voltage in combination with a xed voltage. It isA p roposed in accordance with the invention to obtain the variable biasing potential off the modulation tube by rectification of the current from an oscillator fed from the same network. v

As compared with the known arrangement, the arrangement according to the invention has the advantage that it furnishes the same favorable results in the case of A. C. or D. C. networks. In the hithertoI known arrangement the use of an A. C. supply network was a necessary condition. It would be possible where a D. C. network is present to apply the line voltage to a potentiometer and to derive therefrom the variable biasing potential and the plate potential. But, such an arrangement appears unfeasible in view of the resultant large decrease of the voltage available for the anode. Furthermore, in D. C. supply arrangements the negative pole of the plate potential is ordinarily connected to the positive pole of the heating voltage which condition does not readily permit the insertion of a resistor as potentiometer element for supplying the biasing potential.

In accordance with a further feature of the invention, the oscillator provided for supplying the variable biasing potential is utilized at the same time as excitor or control oscillator for a modulator arrangement. The circuit arrangement assumes an especially advantageous form if this oscillation generator is used as oscillator for the modulator arrangement for which it also This affords the further advantage that other variafurnishes the variable biasing potential.

tions of the high-frequency voltage can likewise (Cl. 17g-171.5)

be compensated such as produced by changes in thecircuit elements of the oscillator. This compensation is possible since the control potential is a direct function of the high-frequency exciter voltage of the modulator.

The invention will be explained in greater detail with reference to Figures 1 and 2 of the accompanying drawing. Figure l shows a tube `transmitter in which the oscillator G and the modulation tube M are separate arrangements, while Figure 2 shows a modification of the invention. In Figure l the audio-frequency modulation voltage NF' is applied to the grid circuit of the modulation tube by means of the transformer TNF. The high-frequency potential I-IF supplied by the oscillator is applied to said grid circuit by means of the transformer THF. The oscillator is represented as tube generator with feed back. Modulator and generator are assumed to be fed' from the same network. In the grid modulation l circuit shown, the non-linear part of the Ia-Vg characteristic is utilized. If the plate potential varies for instance by -l-AVa, the working point changesv its location. This entails a variation of the delivered high-frequency potential, and of the degree of modulation. To provide compensation it is necessary to impress upon the grid an' additional biasing potential equal to -Dnva where D is the reciprocal of the amplification factor of the tube. Thus, due to the plate potential being likewise increased by -l-AVa, the high frequency amplitude will be increased in the oscillator tube by a value proportional to AVa. A high-frequency current is derived from the plate circuit of the oscillator tube by means of a further winding of the transformer THF, said current being rectified by a tube detector or drycontact rectifier. The rectier shown is a dry contact rectifier bridge GI by which a variable direct biasing potential is obtained whose variation in operation is likewise proportional to AVa. If this voltage is caused to coact with the direct biasing potential B of the modulation tube the variations of the plate potential can by proper proportioning be compensated for the high-frequency potential applied to the load Re across the output transformer TA and the modulation factor remain constant.

Another embodiment of the invention is shown in the example of Figure 2. In, this figure the output potential of the oscillator G is applied to the grid circuit of the modulator M by means of connections from terminals l, 2 to the output of the transformer 'I'I-IF, or it may be applied to any other load such as another modulator or a de-modulator by means of terminals I, 2. As compared with the circuit of Figure 1, a considerable simplification resides in that the variable grid biasing potential is derived directly from the oscillation generator. As shown, rectication of the feed back potential is accomplished by the grid-cathode path of the generator tube. The direct current obtained in the gri'd cathode circuit by the rectication between the grid and cathode and owing through resistor Rg causes a potential to be stored in the condenser Cg. This potential is applied through resistor R in series with biasing battery B to the grid of modulator tube M. Resistor R and condenser C act` as a filter network for the direct current obtained from the oscillator circuit. When using a multielectrode tube as oscillator, the rectification may,

however, also be obtained through other suitable electrodes. The oscillator G supplying the variable biasing potential. for the modulator M need not be used necessarily as a generator of the carrier for the modulator M as any other available source of high frequency energy may `be applied to terminals HF if desired.

I claim:

1. A circuit arrangement including a rst thermionic discharge `tube having'a control grid and serving as a generator for high frequency oscillations, a second thermionic discharge tube having a control grid and serving as a modulator tube for high frequency oscillations, means for applying a biasing potential to said control grid of said second tube, means for Iectifying a portion of the oscillations as generated by said first tube and means for applying said rectied oscillations as anV added bias to the control grid of said second tube. 1

2. A circuit arrangement including a iirst thermionic discharge tube having a control grid and serving as a generator for high frequency oscillations, a second thermionic dischargetube having a control grid and serving as a modulator tube for high frequency oscillations, means for applying high frequency oscillations and means for applying modulating potentials to said control grid of said second tube whereby said high frequency oscillations are modulated by said modu-` latlng potentials, means for applying a biasing potential to said control grid of said second tube and means for rectifying a portion of the un modulated oscillations generated by said rst tube and means for applying said rectified oscil of said modulator tube, means for also applying modulating potentials to said grid, means for applying a xed bias to the grid of said second tube and means" for applying a variable added bias `to the grid of said second tube said last mentioned means comprising a connection including a resistance and a condenser connected in shunt thereto between the control vgrid and cathode of said oscillator tube and a connection from the end of said resistance adjacent the control grid of saidoscillator tube to the control grid of said modulator tube whereby the bias applied to the control grid of said modulator tube varies in accordance with the amplitude of the oscillations generated by said oscillator tube.

4. A circuit arrangement including an oscillator circuit, a modulator tube having a control gridY and a plate, meansrfor energizing said oscillator and said modulator including a source of;y I

biasing potential Vfor the` control grid of said modulator tube,means for rectifying a portion of the immediate output of said oscillator and means for applying said rectied output in series with said source of biasing potential as an additional bias. -Y

5. A` transmitter includingA an oscillator circuit, a modulator tube having a control grid and a plate, means for energizing Said oscillator and said modulator including a source of biasing potential for the control grid of said modulator tube, a rectifier immediately coupled to said oscillator circuit and means for connecting said recti- 4 fier in series with said source of biasing potential.

FRIEDRICH KAESER. 

